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Published August 27, 2026. Prices and specs checked September 9, 2026.
A power bank’s mAh rating tells only part of the story. Ten thousand mAh covers one anxious day — a phone dead by 3 p.m. that needs enough left in it to make it through dinner. Twenty thousand mAh covers a full day away from an outlet, or a phone plus a tablet. Neither number is what actually reaches your phone, once voltage conversion takes its cut.
Run the real math on three current power banks: the $25.99 Anker 313 Power Bank (PowerCore 10K), the $36.99 INIU Carry P51L-E2, and the $139.99 Anker Prime 20,000mAh Power Bank (200W). The cheapest 20,000mAh bank here delivers the same usable capacity as the one that costs nearly four times as much. The Prime’s price buys speed and a screen. It does not buy more phone charges.
I’ve ridden out enough hurricane-season power outages to keep a power bank charged by habit. What matters most in those stretches isn’t the number printed on the box. It’s how many real phone charges I can count on before the grid comes back.
What a Power Bank’s mAh Rating Really Costs in Weight and Price
Every mAh figure printed on a power bank is the battery cell’s rating, not what leaves the USB port. Lithium cells run at 3.7 volts. USB charging runs at 5 volts and up. Boosting that voltage costs real capacity before it costs you anything else. Line up rated capacity against a realistic delivered figure, and the ranking on price-per-mAh flips.
| Power bank | Price | Rated capacity | Delivered capacity (~62%) | Cost per 1,000mAh delivered | Weight per 1,000mAh delivered |
|---|---|---|---|---|---|
| Anker 313 Power Bank (PowerCore 10K) | $25.99 | 10,000mAh | ~6,200mAh | $4.19 | 34.3 g |
| INIU Carry P51L-E2 | $36.99 | 20,000mAh | ~12,400mAh | $2.98 | 26.3 g |
| Anker Prime 20,000mAh Power Bank (200W) | $139.99 | 20,000mAh | ~12,400mAh | $11.29 | 43.9 g |
INIU wins both columns. It delivers roughly the same usable capacity as the Anker Prime for a little over a quarter of the price. It also does it lighter per delivered mAh than either Anker. The 313 is the most expensive of the three per delivered mAh. That’s the tax on a bank small enough to disappear in a jacket pocket. It’s 7.5 ounces total, not per thousand mAh.
The Prime’s $11.29-per-1,000mAh number looks bad in isolation, until you remember it isn’t selling capacity. It’s selling 200 watts of output and a display that shows exactly how much charge is left. The $36.99 INIU offers neither at any price.
How Much of a Power Bank’s Capacity Reaches Your Phone?
The gap comes from voltage, not marketing. Cells inside a power bank run at 3.7 volts. A phone charges over USB at 5 volts or higher. So the bank’s own circuitry has to step that voltage up before anything leaves the port. That single conversion step accounts for roughly 26% of the rated capacity on its own. That’s per a physics breakdown published by Power Bank Tests, an independent power bank testing publication. Internal resistance, the boost converter’s own inefficiency, and heat add another several percent on top. That lands a well-made 20,000mAh bank’s realistic yield around 12,000–12,400mAh — the ~62% figure used in the table above.
None of the three makers here publish that adjusted number. Anker and INIU both advertise the cell rating, and it’s accurate — it just isn’t the number that ends up in your phone. We applied that same ~62% yield to all three banks, so treat it as a modeled figure, not a measured one. Real-world yield varies unit to unit, and none of the three brands publish a tested number of their own.
Apple’s iPhone 16 carries a 3,561mAh battery, per GSMArena’s published specifications. Against that reference: the Anker 313’s ~6,200 delivered mAh is good for about 1.7 full charges. The INIU and the Anker Prime each land around 3.5 charges — the same number, from two very differently priced bags.
Matching a Power Bank’s mAh to the Trip, Not the Sticker
A single dead-phone rescue — the 3 p.m. panic — needs one real charge, call it 3,500–4,500 delivered mAh depending on the phone. Even the Anker 313’s ~6,200mAh clears that with room to spare, and at $25.99 it’s the cheapest way in this comparison to solve exactly that problem.
A full day away from an outlet, or splitting charges between a phone and a smaller device like earbuds or a watch, runs closer to 8,000–10,000 delivered mAh. That rules the 313 out. It puts both 20,000mAh-rated banks — INIU and the Prime — in the running. Each carries more than enough delivered capacity for that job alone.
Tom’s Guide’s Jason England, who reviews power banks professionally, draws a similar line: “Personally, I won’t go below 10,000mAh if I’m charging my phone more than once a day,” he wrote in the outlet’s portable charger buying guide. That’s a rated number, not a delivered one — which puts his real floor closer to 6,000mAh usable, in line with what the math above says a 10,000mAh-rated bank actually clears.
Charging a laptop is a different question, and capacity alone doesn’t answer it.
Can These Power Banks Charge a Laptop?
Capacity is only half of a laptop’s charging question; wattage decides the other half. USB Power Delivery is the standard all three of these banks use. It scales in defined tiers up to 100W, 140W, 180W, and 240W, per the USB Implementers Forum’s own specification. Most mainstream laptops charge at a genuinely usable speed somewhere in the 45–65W range. HP, for one, ships most of its own laptops with a 65W charger and says a lower-wattage one “will still work, but it may charge slowly.”
Of the three banks here, only the Anker Prime’s 200W output clears that bar with room to spare. It’s rated to take a 16-inch MacBook Pro to 50% in about 40 minutes, per Anker’s own listing. INIU’s 45W output can keep a laptop from losing ground during light use, but it won’t fast-charge one. The Anker 313’s 15W is a phone-and-earbuds number; plugging a laptop into it barely dents the drain.
Power Bank mAh Limit on Planes
Air travel puts a hard ceiling on power bank size, and the ceiling is set in watt-hours, not mAh. The FAA’s PackSafe page says spare lithium batteries, power banks included, “must be carried in carry-on baggage only.” It also limits rechargeable lithium-ion batteries to “a rating of 100 watt hours (Wh) per battery.” With airline approval, a passenger may carry up to two larger spares, in the 101 to 160 Wh range.
Converting is simple. The FAA’s instruction is to multiply battery voltage by amp-hours. A 20,000mAh bank is 20 Ah, and at the 3.7-volt cell rating used above, 20 × 3.7 = 74 Wh. That clears the 100 Wh line, and so do all three banks here. Run the same arithmetic backward and the ceiling lands near 27,000mAh, because 100 ÷ 3.7 is about 27 Ah.
Airlines can set stricter limits, including a cap on how many power banks you bring, so check your carrier before you fly. And if a carry-on gets checked at the gate, the FAA says the spare batteries must come out of the bag and stay with you in the cabin.
Where Each Power Bank Falls Short
Skip the Anker 313 if you need it to double as a tablet or laptop charger. Fifteen watts is a phone number, full stop. Anker’s own listing doesn’t specify a warranty length for this model, which is unusual for the brand. It’s worth asking about before you buy if that matters to you.
Skip the INIU if footprint is the priority over price. At 11.5 ounces for 20,000mAh rated, it’s heavier than the value math above makes it look. That’s because a 45W output needs sturdier internal wiring than a 15W bank does. It also has no display, so there’s no way to check remaining charge without plugging in a phone.
Skip the Anker Prime if you’re only ever charging a phone. Paying $139.99 for a screen and 200 watts of headroom you never use has a cost. It turns a $2.98-per-1,000mAh problem into an $11.29-per-1,000mAh one. That’s for the same delivered capacity as a bank that costs a quarter as much.
Which Power Bank Would I Buy?
Humid outdoor days on the coast have taught me to keep phones and earbuds topped off, not maxed out. So if I were buying tonight for a phone-only bag, it’s the INIU Carry P51L-E2. It delivers the Prime’s usable charge for a quarter of the price. Bring a laptop along and the math changes — the Prime earns its price. The 313 is the only one of the three I’d rule out for anything past a strict emergency-only role.
Prices are approximate, current as of publication, and change frequently — confirm the latest price with the retailer before buying.
For more on what’s actually worth paying for in a charging accessory, see our comparison of 3-in-1 nightstand wireless chargers and our breakdown of which smartwatches go weeks instead of days between charges. Browse more of our smart home comparisons for other charging and accessory picks.
